The objective of this contract is to maintain and update the data files of the Child Health and Development Studies (CHDS). The Child Health and Development Study (CHDS) of 20,000 pregnancies began in 1959, as a companion to the Perinatal Collaborative Study. The NICHD provides support to maintain the CHDS database and serum collection. Investigators who are interested in maternal and placental origins of disease later in life currently use these resources, especially in the study of long-term effects of in utero exposure to organochlorines, such as dichlorodiphenyltrichloroethane or DDT (Cohn et al 2003).[unreadable]